Early development of the mammalian eye proceeds through a series of mutual inductive interactions involving the surface and neural ectodermal layers of the embryo. Defects in these events lead to a number of human eye malformations, including microphthalmia and clinical anophthalmia, congenital cataracts and glaucoma, and anterior segment dysgenesis syndromes. The genetic control of these events is poorly understood at present. However, recent findings suggest that key proteins controlling early pattern formation in the eye may be broadly conserved throughout metazoan evolution, from Drosophila melanogaster to humans, despite significant structural and functional differences. Mutations in the PAX6 transcription factor are associated with aniridia and anophthalmia in humans, the Small- eye cataracts phenotype in mice, and the eyeless phenotype in Drosophila. Similarly, the sine oculis gene product is required for eye formation in Drosophila and its mammalian homolog (Six-3) is a potent regulator of vertebrate lens induction. This proposal will use molecular, genetic, histological, and cellular methods to explore to the function of homologs to the Drosophila eyes-absent gene (eya), which is required downstream from PAX6 in the eye imaginal disc for progression of the morphogenetic furrow. In preliminary studies, we have successfully cloned a family of mammalian genes with striking sequence nomology to eya. Tide encoded proteins define a new 274-amino acid domain structure. Interestingly, one of these loci (Meya-1) is specifically made in the mouse eye, with maximal expression at day El1.5 in utero, and maps close to a dominant cataracts locus on chromosome 2. These observations further suggest the existence of a conserved pathway with shared molecular interactions. The Specific Aims of this proposal will detail the timing and tissue expression pattern, gene structure, chromosomal location, mutant phenotypes of the mouse Meya gene family; test the role of Meya-1 in human congenital eye malformations; examine properties, protein-protein interactions, and binding partners of the conserved eya domain; and explore hierarchical relationships among PAX6, Six-3 and Meya-1. These studies should yield valuable new information concerning the pathogenesis of eye disease and may provide a foundation for better diagnosis and prevention in the future.